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Life in the Universe• This is a long lecture but mostly not “astronomy” and more

“fun” topics. Only the astronomy, which planets and stars

are best suited for life, will be on exams.

• 1 example of Life - Carbon-water based (on Earth)

• 1 example of “intelligence” → able to communicate with other

“intelligent” life for about 80 years (us humans)

• Intelligence = able to use Radio to send/receive messages across space

• chemical building blocks (amino acids, water) plentiful in interstellar

space

• Somehow about 1 billion years after Earth formed, bacteria appeared.

All other life are probably descendants

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Life – Carbon+Water based?

“Ammonia! Ammonia!”

@R. Grossman 1962 New Yorker

Carbon vs Silicon? NO

Water vs other liquid or

gas? Not sure but water

seems to be the best

medium

Carbon makes long chains but

with H and OH not too tightly

bound. Silicon makes rocks as

tightly bound

3

Life on Earth• 4.5 billion years ago Earth formed.

About 1.5 billion years after that

simple bacteria (prokaryote) appeared

• About 2 billion years after, complex

life (eukaryote) appeared including

algae which though photosynthesis

started releasing oxygen

• atmosphere changed, probably

keeping planet warm enough so end

of periodic “iceball Earth”??

→ Takes billions of years

for complex life to

develop. Lesson for

PHYS 162 (don’t need to know

biology for this course)

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Life on Earth (don’t need to know

for this course)• appears all current life descended from same ancestor

• all use DNA and RNA and amino acids

• all use ATP for storing/using energy

• amino acids come in both left-handed and right-handed

versions. All Earth life uses left-handed exclusively

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Other Life in Solar System?

• there is, or has been, liquid water on Mars and

various moons of Jupiter (Europa, Ganymede,

Callisto) and Saturn (Titan, Enceladus)→ look for

signs of life.

• If ever find, is it of different origin then Earth’s?

• more info about Mars then anywhere else: meteors

from Mars and landings on the surface. No evidence

yet

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Best Bet: Moons of Jupiter and Saturn

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Life on Mars?• landings on the surface have probably not shown any evidence (2019

article that is not yet published has title “Evidence of life on Mars?”

which admits the evidence is circumstantial). That there was liquid

water means life probably did exist either Mars- or Earth-origin.

• BUT 16 million years ago, an asteroid slammed into Mars, Mars

rock thrown into space, drifted, and landed in Antarctica 13,000 years

ago, analyzed starting in 1996

• tell from Mars by chemical and gas composition

• possible indications (tubelike objects, hydrocarbons) of bacteria

fossils from 3.6 billion years ago

• no agreement among experts

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Extra Terrestrial Intelligence• is there intelligent life on other planets?

Drake equation (~1962, Frank Drake who later worked with Carl

Sagan) estimates possibility in our galaxy. Carl Sagan and Joan Allen

were speakers at 1995 NIU 100th anniversary event. DH was Sagan’s

escort for the day. DH suggested to Sagan to add the phrase “and

possible infinite number of Universes” to Sagan’s catchphrase of

“billions and billions of stars in billions of galaxies”. Sagan did at his

NIU talk and those he gave before he died but did not give DH any

credit.....DH also introduced Sagan to Joan Allen our NIU alumnus

who has been nominated for an Academy award twice who sort of

blew her off until he realized she was famous

• can we try to communicate?

SETI = Search for Extra Terrestrial Intelligence

For this course define intelligence as the ability to communicate by radio

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Drake Equation

• N = number of “intelligent” civilizations in the Galaxy at

any given time

• R* = rate at which solar type stars are formed

• fp = fraction of stars which have planets

• ne = number of planets suitable for life

• fl = fraction of planets where life arises

• fi = fraction of life that develops intelligence

• fc = fraction of intelligent life that communicates by radio

• L = lifetime of communicating intelligence

First three (in red) are astronomy questions, rest (in green)

biology, anthropology, sociology

LfffnfRN cilep=

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Possible Stars + Planets

Stars can’t be

• too large. Need lifetime more than 2 billion years and so

stars like our Sun or smaller are stable main sequence stars

for that amount of time or longer

• too small. habitable region is too close to star. See next

slide on planets

• too old. Need heavy elements C,O,N which are formed in

Red Giants or supernovas. The oldest stars are just

Hydrogen and Helium

• in binary system. Planet’s temperature varies as getting

energy from 2 or 3 stars. Also can have complicated orbits

for both the stars and the planets

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Possible Stars + PlanetsPlanets can’t be

too large or too small. want right atmosphere. Best guess

is Earthlike

too hot or too cold. want temperature so liquid water

To close to their star: tidal forces tend to have one side of

planet always facing its star. Solar flares from small

stars are the same intensity as flares from our Sun. If

planet is too close the flare would be destructive to any

existing life

→ habitable zone about a star. Where water may be

liquid if other conditions (size/atmosphere) are right

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Habitable

Zone: further away if

star more

luminous, closer

if less luminous

Hotter stars

Our Solar System

Cooler stars

Green region

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Habitable Zone – Some Exoplanets

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Nearest Stars

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Nearby Stars• Most are smaller red stars with habitable zone very close to star

→ NOT good places for life to develop

gravitational pull → larger tidal forces → slow/stop planet spin

Stellar flares similar to Sun’s → large radiation blasts on planet

• Stars similar to Sun (Procyon, Sirius, Alpha Centauri) are parts of

binary systems or filled with debris (t Ceti) or young (e Eridani) or

metal deficient (t Ceti and e Eridani)

→ NOT good places for life to develop

Binary systems: too much variation in energy received on planet and

varying gravitational forces slow/stop planet’s spin

→ No close-by star is probably a good place to visit ET. See link on

course web page (plus preview of movie Battleship where aliens came

from a nearby star….probably not)

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Evolution of Intelligence+ Technology

not astronomy questions

• Probability of evolution: simple to complicated to intelligent life?

• How probable is the development of technology?

DH:NOT VERY Carl Sagan: VERY

• dolphins do not need technology

• How did humans evolve?

opposable thumb. Good for grasping, throwing (humans are the only

animal capable of throwing an object, say a baseball, at 100 mph)

very good communication

physically slow and weak though with good endurance and so need

to “do something” to survive → use tools

tools → technology (defined as “modern” tools such as radio) in some

cultures but not in others. Why?

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Length of Survival of “Intelligence”• for human culture, anyone’s guess. 100 to 100,000,000

years. Critical element in Drake equation and whether or

not ET is still around should we receive a signal

• large asteroid: 1 of 5 previous mass extinctions on Earth.

Gets all the headlines. Is the “astronomy” item

• Large volcano: 4 of 5 mass extinctions (Yellowstone

next?). Some geologists believe the asteroid extinction was

really due to another volcano extinction (Deccan in India).

• environmental catastrophes (global warming, ozone,

insecticides)

• nuclear/biological war

• Plague including new viruses or bacteria

On assignment, your guess on what will destroy us

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Length of Survival of “Intelligence”Most species are extinct

• In last 70 years we have almost destroyed ourselves

- nuclear war (1962, 1982, still threat)

- pesticides (similar to human hormones. reduce fertility, may still be

problem, see link on web page)

- destroy ozone layer (governments intervened)

- climate change (governments unable/unwilling to intervene, still a

problem, gotten worse in last 4 years do to changes in US policies)

- pandemics. 2009 H1N1, 2014-2016 Ebola, 2020-2021 COVID-19.

COVID-19 is deadlier than H1N1 but much less deadly than Ebola.

The Ebola outbreak was managed by strong European and US

responses directly to Africa to contain the virus, and strict quarantine

for travelers. Imagine if an Ebola-like virus had arisen in 2020.

Effective government response can make a difference. Note in 2020

New Zealand, Germany, Taiwan all have female leadership.

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Asteroids, Comets and MeteorsMeteor crater in

Yucatan, from

65,000,000

years ago for

extinction

event, maybe

end of

dinosaurs

Meteor crater in Arizona, from

50,000 years ago

type frequency size destructive force

Localized 1/200 yrs 100 m 300 kton

Regional 1/100,000 yrs 1 km mag 12 earthquake

Global 1/20,000,000 yrs 10 km extinction

19 mile wide crater under

Antarctica ice from 800 m

wide meteor which struck 1

million years ago discovered

in 2018

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Asteroids, Comets and Meteors

Can be bumped out of orbit in

asteroid belt mostly by Jupiter

Some comets have very

elliptical orbit and so

can cross Earth’s orbit

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Near Earth Asteroid NEA

Look for and track all objects which pass close to Earth. ~1500

are “potentially hazardous”. Most new telescopes, like Dark

Energy Survey, also look for and track nearby objects. But a car-

sized asteroid came within 1800 mile of Earth on August 16, 2020

and no one spotted it until it was leaving the vicinity. A smaller

asteroid was spotted (7 feet); almost hit us on Nov 2, 2020.

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How Asteroids will Kill You

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Near Earth Asteroids(29075) 1950 DA is notable for having the highest known

probability of impacting Earth (between 0 and 0.33%). Would

happen on March 16, 2880. But orbit can change with time....

Nearby asteroids

Year mass size

2880 3 billion tons 1 km

2011 flyby 130 million tons

2013 flyby 130,000 tons 45m

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Near Earth Asteroids - Defense?

Ala movies: some research going in to how to destroy/deflect an

asteroid if it looks like it will hit the Earth. See Physics Today article

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Greenhouse Effect with Methane and Carbon

Dioxide went over in detail earlier

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Drake Equation – guess at values – get

number of CURRENT civilizations

• R* = rate at which solar type stars are formed 1 per year

• fp = fraction of stars which have planets 0.5 - 1

• ne = number of planets suitable for life 0.01 - 0.1 ??

• fl = fraction of planets where life arises 0.001 - 0.1 ?????

• fi = fraction of life that develops intelligence 0.0001 - 0.5 ???????

• fc = fraction of intelligent life that communicates 0.0001- 0.9 ??????

• L = lifetime of communicating intelligence 100 - 250,000 years ???

• N = # of “intelligent” civilizations currently in the Galaxy =

1000 (optimistic) OR = 1 (us possibly realistic).

Guesses are mostly DH’s (mine). In 50-100 years the number of

suitable planets will probably be much better understood

• Communicate=receive/send radio signals

SLIDE FOR ASSIGNMENT 7

LfffnfRN cilep=

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Communicating with ET

• send a spaceship

too slow. velocity is at most .001 times light speed so

more than 3000 years to nearest star. Movie Passengers

• send a radio/TV message (and listen for them)

travels at speed of light over a wide area

What frequency?

What message?

What direction? maybe in time have a list of found

nearby Earth-like exoplanets (purpose of TESS project)

and have studied their atmospheres with possible

indications of life

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Communicating with ET spacecraft

• covers why

space travel

will always be

“slow”

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Communicating with ET: spacecraft

• Pioneer 10+11 and

Voyager I+II launched

in 1973+1977

• Now beyond Pluto. Can

still communicate with

the Voyager crafts at

117 AU from Sun

• contain plaques and

records for ET to find

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Pioneer plaque. Drake and Sagan design. Very

controversial as humans are unclothed (!), not

generic enough, and the male is dominant. Also

our position is being given to the aliens and so

they will be able to find us and attack us (not a

joke)

• Voyager record includes “Hello” in

many languages, Richard Nixon,

and 90 minutes of music from

Javanese to Bach to Chuck Berry.

Sagan chaired committee. Also

controversial as had “rock&roll”

• Old SNL joke. first message from

aliens “send more Chuck Berry”

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Communicating with ET: RadioWhat frequency? Microwave is most quiet. One

of water’s frequencies? 21 cm often choice

Humans have been sending out

radio signals for about 80 years. As

travel at the speed of light now 80

LYs away, and covers about

0.00001 (1 part in 100,000) of the

Milky Way galaxy. If an alien

civilization lasted less than about

100,000 years, if we detect any

signal from them, they are probably

still not broadcasting and not able

to receive a reply from us.

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Communicating with ET: Radio

What message? In SciFi humans and aliens can communicate (2016

movie Arrival). In reality we have “lost human languages”

(Mayan, Egyptian without Rosetta Stone). In movie Contact (from

Carl Sagan’s book). Signal sent in 1974 by Arecibo in Puerto Rico

23 columns by 73 rows = 1679 bits (either 0 or 1). 2 prime

numbers. repeated pattern. No “color” just on or off for different

bits. Aliens should recognize 2 odd numbers and pattern

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numbers 1 to 10

elements H (1) C(6) N(7) O(8) P(15)

nucleotides (like phosphate and adenine)

DNA double helix including the number of base

pairs in human genome (looks like antenna

coming out of human’s head)

human with height (left) and population (right)

9 planets plus Sun with Earth shifted

Arecibo telescope with diameter noted on bottom

Could we figure this out if not given the answer?

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Lecture FeedbackE-mail me a few sentences describing one topic you learned from

this set of presentations. Please include the phrase “Stars the size

of our Sun or smaller are felt to be the best candidates for life

outside our Solar System as they have long enough lifetimes

exceeding billions of years ” in your mini-report but do not use

that as your “one topic”.